None of these are EVOLUTIONARY ALGORITHMs, but all of them use the
evolutionary metaphor as their "playing field".
Tierra
Synthetic organisms have been created based on a computer metaphor of
organic life in which CPU time is the ``energy'' resource and memory
is the ``material'' resource. Memory is organized into informational
patterns that exploit CPU time for self-replication. MUTATION
generates new forms, and EVOLUTION proceeds by natural SELECTION as
different GENOTYPEs compete for CPU time and memory space.
Observation of nature shows that evolution by natural selection is
capable of both OPTIMIZATION and creativity. Artificial models of
evolution have demonstrated the optimizing ability of evolution, as
exemplified by the field of GENETIC ALGORITHMs. The creative aspects
of evolution have been more elusive to model. The difficulty derives
in part from a tendency of models to specify the meaning of the
``genome'' of the evolving entities, precluding new meanings from
emerging. I will present a natural model of evolution demonstrating
both optimization and creativity, in which the GENOME consists of
sequences of executable machine code.
From a single rudimentary ancestral ``creature'', very quickly there
evolve parasites, which are not able to replicate in isolation
because they lack a large portion of the genome. However, these
parasites search for the missing information, and if they locate it
in a nearby creature, parasitize the information from the neighboring
genome, thereby effecting their own replication.
In some runs, hosts evolve immunity to attack by parasites. When
immune hosts appear, they often increase in frequency, devastating
the parasite POPULATIONs. In some runs where the community comes to
be dominated by immune hosts, parasites evolve that are resistant to
immunity.
Hosts sometimes evolve a response to parasites that goes beyond
immunity, to actual (facultative) hyper-parasitism. The hyper-
parasite deceives the parasite causing the parasite to devote its
energetic resources to replication of the hyper-parastie genome.
This drives the parasites to extinction. Evolving in the absence of
parasites, hyper-parasites completely dominate the community,
resulting in a relatively uniform community characterized by a high
degree of relationship between INDIVIDUALs. Under these
circumstances, sociality evolves, in the form of creatures which can
only replicate in aggregations.
The cooperative behavior of the social hyper-parasites makes them
vulnerable to a new class of parasites. These cheaters, hyper-hyper-
parasites, insert themselves between cooperating social individuals,
deceiving the social creatures, causing them to replicate the genomes
of the cheaters.
The only genetic change imposed on the simulator is random bit flips
in the machine code of the creatures. However, it turns out that
parasites are very sloppy replicators. They cause significant
RECOMBINATION and rearrangement of the genomes. This spontaneous
sexuality is a powerful force for evolutionary change in the system.
One of the most interesting aspects of this instance of life is that
the bulk of the evolution is based on adaptation to the biotic
ENVIRONMENT rather than the physical environment. It is co-evolution
that drives the system.
--- "Tierra announcement" by Tom Ray (1991)
How to get Tierra?
Tierra is available (source and executables, for Unix and NT) from
alife.santafe.edu/pub/SOFTWARE/Tierra
.
Related work
David Bennett <dmb@pfxcorp.com> reported in March 2000: Much new work
has been done in Tierra since 1993. Thomas Ray
<tray@mail.nhn.ou.edu> is now working in Japan. I have been using
another similar system called Avida. It has some advantages, and a
significant body of research results. The contact for Avida is
<avida@krl.caltech.edu>.
References
Ray, T. S. (1991) "Is it alive, or is it GA?" in [ICGA91], 527--534.
Ray, T. S. (1991) "An approach to the synthesis of life." in
[ALIFEII], 371--408.
Ray, T. S. (1991) "Population dynamics of digital organisms." in
[ALIFEII].
Ray, T. S. (1991) "Evolution and optimization of digital
organisms." Scientific Excellence in Supercomputing: The IBM 1990
Contest Prize Papers, Eds. Keith R. Billingsley, Ed Derohanes, Hilton
Brown, III. Athens, GA, 30602, The Baldwin Press, The University of
Georgia.
Ray, T. S. (1992) "Evolution, ecology and optimization of digital
organisms." Santa Fe Institute working paper 92-08-042.
Ray, T. S. "Evolution, complexity, entropy, and artificial reality."
submitted Physica D.
Ray, T. S. (1993) "An evolutionary approach to synthetic biology,
Zen and the art of creating life. Artificial Life 1(1).
VENUS
Steen Rasmussen's (et al.) VENUS I+II "coreworlds" as described in
[ALIFEII] and [LEVY92], are inspired by A.K. Dewdney's well-known
article (Dewdney 1984). Dewdney proposed a game called "Core Wars",
in which hackers create computer programs that battle for control of
a computer's "core" memory (Strack 93). Since computer programs are
just patterns of information, a successful program in core wars is
one that replicates its pattern within the memory, so that eventually
most of the memory contains its pattern rather than that of the
competing program.
VENUS is a modification of Core Wars in which the Computer programs
can mutate, thus the pseudo assembler code creatures of VENUS evolve
steadily. Furthermore each memory location is endowed with
"resources" which, like sunshine are added at a steady state. A
program must have sufficient resources in the regions of memory it
occupies in order to execute. The input of resources determines
whether the VENUS ecosystem is a "jungle" or a "desert." In jungle
ENVIRONMENTs, Rasmussen et al. observe the spontaneous emergence of
primitive "copy/split" organisms starting from (structured) random
initial conditions.
--- [ALIFEII], p.821
Dewdney, A.K. (1984) "Computer Recreations: In the Game called Core
War Hostile Programs Engage in a Battle of Bits", Sci. Amer. 250(5),
14-22.
Farmer & Belin (1992) "Artificial Life: The Coming Evolution",
[ALIFEII], 815-840.
Rasmussen, et al. (1990) "The Coreworld: Emergence and Evolution of
Cooperative Structures in a Computational Chemistry", [FORREST90],
111-134.
Rasmussen, et al. (1992) "Dynamics of Programmable Matter",
[ALIFEII], 211-254.
Strack (1993) "Core War Frequently Asked Questions (
rec.games.corewar FAQ)" Avail. by anon. FTP from
rtfm.mit.edu/pub/usenet/news.answers/games/corewar-faq.Z
PolyWorld
Larry Yaeger's PolyWorld as described in [ALIFEIII] and [LEVY92] is
available via anonymous FTP from
alife.santafe.edu/pub/SOFTWARE/Polyworld/
"The subdirectories in this "polyworld" area contain the source code
for the PolyWorld ecological simulator, designed and written by Larry
Yaeger, and Copyright 1990, 1991, 1992 by Apple Computer.
PostScript versions of my ARTIFICIAL LIFE III technical paper have
now been added to the directory. These should be directly printable
from most machines. Because some unix systems' "lpr" commands cannot
handle very large files (ours at least), I have split the paper into
Yaeger.ALife3.1.ps and Yaeger.ALife3.2.ps. These files can be ftp-ed
in "ascii" mode. For unix users I have also included compressed
versions of both these files (indicated by the .Z suffix), but have
left the uncompressed versions around for people connecting from non-
unix systems. I have not generated PostScript versions of the
images, because they are color and the resulting files are much too
large to store, retrieve, or print. Accordingly, though I have
removed a Word-formatted version of the textual body of the paper
that used to be here, I have left a Word-formatted version of the
color images. If you wish to acquire it, you will need to use the
binary transfer mode to move it to first your unix host and then to a
Macintosh (unless Word on a PC can read it - I don't know), and you
may need to do something nasty like use ResEdit to set the file type
and creator to match those of a standard Word document (Type = WDBN,
Creator = MSWD). [..]"
--- from the README by Larry Yaeger <larryy@apple.com>
General Alife repositories?
Also, all of the following FTP sites carry ALIFE related info:
ftp.cognet.ucla.edu/pub/alife/ ,
life.anu.edu.au/pub/complex_systems/alife/ ,
ftp.cogs.susx.ac.uk/pub/reports/csrp/ , xyz.lanl.gov/nlin-sys/ ,
alife.santafe.edu/pub/ .

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